Biotic recovery after the end-Triassic extinction event: Evidence from marine bivalves of the Neuquén Basin, Argentina

Abstract

We analyze the Late Triassic extinction and Early Jurassic recovery of bivalve faunas within marine environments in the Atuel River area of the Neuquén Basin, Argentina. Data were collected from a hundred samples with invertebrates in a well-exposed uppermost Triassic to lower Jurassic section in the Neuquén Basin (southern Mendoza Province, Argentina) and allow a high-resolution reconstruction of the local diversity dynamics. The nearly continuous presence of marine stenohaline major taxa such as cnidarians, rhynchonelliform brachiopods, echinoderms and cephalopods indicates normal salinity throughout. All bivalve species were identified, and each occurrence was recorded in meters above the base. To analyze the systematic diversity trends, diversity curves were calculated on the basis of the first and last occurrence data for each bivalve species, and both total diversity and boundary crossers diversity were used. As a result, four main phases were identified: a) Triassic equilibrium phase (Rhaetian), with relatively high origination and extinction rates; b) extinction phase (latest Rhaetian to earliest Hettangian), with high extinction rates and low origination rates; c) recovery phase (late Early to early Late Hettangian), with high origination rates and almost null extinction rates; and d) Jurassic equilibrium phase (Late Hettangian-Sinemurian), again with similar and relatively high origination and extinction rates. The extinction and recovery phases are separated by a gap of about 135 m without identifiable benthonic invertebrates but with early Hettangian ammonites. On the other hand, bivalve palaeoecologic diversity seems to have been more homogeneous along the section, being dominated by attached epifaunal species, though before the extinction epifaunal habits were slightly surpassed by infaunal ones. Slight differences observed include a) shallow burrowers were more diverse during the Rhaetian than during the earliest Jurassic and b) epifaunal free-lying and semi-infaunal attached bivalves were more diverse after the Rhaetian extinction.

Body size trends and recovery amongst bivalves following the end-Triassic mass extinction

“…Johnson (1984) Panthalassic records of bivalves from the South America have received considerable attention (e.g. Aberhan, 1994;Damborenea, 1987aDamborenea, , 1987bDamborenea et al, 2017), although temporal size data is mostly absent.…”

How quick was marine recovery after the end-Triassic mass extinction and what role did anoxia play?

“…High diversity shell beds with low dominance and highly specialised forms are reported from early Hettangian of Tibet (Hautmann et al, 2008). In the Neuquén Basin, Argentina, recovery appears slower than Tibet, because there is an interval barren of bivalves roughly equivalent to the planorbis Zone, followed by rising diversity and increased occupation of tiering until the canadensis Zone equivalent to the upper angulata Zone (Damborenea et al, 2017).…”

“…Such a simple measure is not suitable for the British record of the recovery from the end-Triassic mass extinction, because diversity in the pre-extinction interval was low due to unusual salinities that were quite different to the fully marine settings that develop in the aftermath (Hallam and El Shaarawy, 1982). A period of rising diversity followed by stabilisation may provide a better assessment of the recovery interval (Damborenea et al, 2017). An alternative four-phase model for recovery, incorporating ecological parameters, was created based on observations of the recovery following the end-Permian mass extinction (Twitchett, 2006, referred to here as the Twitchett recovery model).…”

New insights into the earlier evolutionary history of epiphytic macrolichens

“…In contrast, the diversification of the crown clades of extant conifers, between 190 and 160 Mya in the Early to Middle Jurassic (Leslie et al, 2018), coincides well with the 165 Mya Daohugouthallus ciliiferus fossil, thus providing the earliest known evidence of the existence of epiphytic macrolichens. Notably, various other groups of organisms underwent radiations in this period, such as mammals or the avian stem lineage (Benson et al, 2014;Close et al, 2015). The Mid-Mesozoic era was a cooling and greenhouse period (Willis and Niklas, 2004) and the palaeoenvironment of the Daohugou formation has been described as humid, warm-temperate and montane (Ren and Krzeminski, 2002;Tan and Ren, 2002;Zhang et al, 2006), thus favoring the potential growth of epiphytic macrolichens, as shown by the ecology of extant macrolichen lineages in the tropics.…”